1. Field of the Invention
The present invention relates to wireless terminal devices and more particularly relates to a method and computer program for communicating, transferring or handing off mobile devices between wireless infrastructure systems without substantially impairing the performance of delay and loss sensitive network applications.
2. Discussion of the Background
Communications networks, such as local area networks (“LAN”) or wide-area networks (“WAN”) allow connected devices to access network applications over the network. For instance, the Internet is a global network of connected computer networks providing network applications and data content to connected devices. Connected devices may include, without limitation, desktop computers, laptop computers, servers, palmtop or other hand-held computers, personal digital assistants, Internet enabled mobile phones, pagers, digital capturing devices (e.g., digital cameras and video cameras), Internet appliances, e-books, wireless sensor devices and the like. Connected devices are connected to the wired and wireless networks using numerous techniques known in the art. For instance, mobile devices are commonly connected to a computer network using radio technology in communication with a wireless system, such as a wireless access point (“WAP”), a cellular base station or the like that is connected to the Internet.
The radio communication between a mobile device and a wireless system may deteriorate due to various factors including, without limitation, communication range, signal interference and movement of the mobile device with respect to the wireless system. Wireless systems typically have a limited communication range varying from one hundred meters or less for WAPs to several miles for wireless systems utilizing cellular telephony.
As is generally known in the art, in order for a mobile device to communicate with a wireless system, it must first find one or more wireless systems. The process of finding a wireless system is known as service discovery. Active service discovery requires the mobile device to broadcast PROBE REQUEST messages over one or more channels. If a wireless system is within the mobile device's communication range, the wireless system responds by transmitting a PROBE RESPONSE to the mobile device. Not every wireless system within the communication range of the mobile device will respond to a PROBE REQUEST. For instance, the responding wireless systems may be limited to those wireless systems matching one or more parameters of the inquiry. The response from a wireless system generally will include information necessary for the mobile device to access the network including a description of the network. The mobile device will process the responses received from the wireless systems within the communication range of the mobile device. After receiving the responses to the PROBE RESPONSE, the mobile device will have accumulated information about the wireless systems within communication range of the mobile device. Once a mobile device has performed an PROBE RESPONSE, the mobile device may choose to join a network via one of the available wireless systems.
After joining a network, the mobile device may transmit and receive data across the network using radio technology or the like via the wireless system. If the communication between the mobile device and the wireless system fails before the completion of a transmission, then the data may be irretrievably lost. For instance, if the mobile device physically moves out of the communication range of a wireless system, then any communication between the mobile device and the wireless system will fail. Network communication is either lost or the session is severely degraded as the mobile device moves out of the vicinity and, thus, the beyond the communication range of the wireless system through which the mobile device is communicating.
A handoff is the process of transferring the communication process of a mobile device from one wireless system to another wireless system. Current technologies, such as those technologies that do not have dedicated control channels to communicate with network infrastructure, do not adequately handle communication with mobile devices while handing off the mobile device. Currently available handoff solutions incur roaming delays of between approximately 120 milliseconds to several seconds. Additionally, if the mobile device is required to join a different subnet, the handoff may incur additional delays of approximately 1-2 seconds or more.
A handoff may require allocation of a new IP address. The dynamic host configuration protocol (“DHCP”) or IPv6 provides for the dynamic allocation of an IP address to a host, such as a mobile device, in a transmission control protocol/Internet protocol (“TCP/IP”) network. Dynamic allocation is particularly useful for assigning an IP address to a host that will be connected to a network only temporarily or for sharing a limited pool of IP addresses among a group of hosts that do not need permanent IP addresses. The period over which an IP address is allocated to the host is referred to as a “lease.”
Communication failures associated with current handoff solutions are especially problematic for delay sensitive network applications such as Voice-over-IP (“VoIP”), streaming multimedia and other real-time data services. Such delay sensitive network applications demand seamless and continuous network connectivity. The inter-packet delay for these applications typically ranges from approximately 50 milliseconds for demanding applications, such as VoIP, to approximately 150 milliseconds for less demanding applications, such as audio/video real-time streaming with frame coding (e.g., at 64K bps). Current handoff solutions of systems without dedicated control channels result in the loss of data packets which is clearly unacceptable for delay sensitive applications. There does not currently exist a way to reduce the time required to handoff a mobile device for these type of systems.
The Institute of Electrical and Electronics Engineers (“IEEE”) 802.11 standard is commonly used for radio communication between a mobile device and a wireless system. The IEEE standard currently defines the specifications for a 802.11 media access control (“MAC”) protocol and the RF-oriented physical parameters. However, the IEEE standard lacks a standardized roaming algorithm for the handoff of mobile devices between wireless systems. The IEEE standard also does not provide a dedicated control channel between the mobile device and wireless network. A proposed IEEE standard, referred to as IEEE 802.11r, advocates multi-vendor compatibility of wireless hardware devices and improved inter-wireless system communication messages. However, the proposed IEEE 802.11r standard does not adequately solve the handoff of a mobile device. For instance, implementations of the proposed IEEE 802.11r standard require upgrading and/or replacing already deployed wireless systems (e.g., wireless access points). This is an unsuitable solution because there currently exist approximately 30 million wireless systems using the 802.11 standard which would have to be upgraded and/or replaced.
Thus, there does not exist an effective way in the prior art to handle transmissions over a computer network during a handoff between wireless systems.